Unirhinal Olfactory Testing for the Diagnostic Workup of Mild Cognitive Impairment

Article type: Research Article

Authors: Huart, Caroline^{a; b; *} | Rombaux, Philippe^{a; b} | Gérard, Thomas^c | Hanseeuw, Bernard^{a; d} | Lhommel, Renaud^{a; c} | Quenon, Lisa^a | Ivanoiu, Adrian^{a; d} | Mouraux, André^a

Affiliations: [a] Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels, Belgium | [b] Department of Otorhinolaryngology, Cliniques universitaires Saint-Luc, Brussels, Belgium | [c] Department of Nuclear Medicine, Cliniques universitaires Saint-Luc, Brussels, Belgium | [d] Department of Neurology, Cliniques universitaires Saint-Luc, Brussels, Belgium

Correspondence: [*] Correspondence to: Caroline Huart, Avenue Mounier 53 bte B1.53.02, 1200 Brussels, Belgium. Tel.: +32 2 764 54 49; Fax: +32 2 764 54 65; caroline.huart@uclouvain.be

Abstract: Background: Olfactory dysfunction is associated with Alzheimer’s disease (AD), and already present at pre-dementia stage. Objectives: Based on the assumption that early neurodegeneration in AD is asymmetrical and that olfactory input is primarily processed in the ipsilateral hemisphere, we assessed whether unirhinal psychophysical and electrophysiological assessment of olfactory function can contribute to the diagnostic workup of mild cognitive impairment (MCI). Methods: Olfactory function of 13 MCI patients with positive amyloid PET, 13 aged-matched controls (AC) with negative amyloid PET and 13 patients with post-infectious olfactory loss (OD) was assessed unirhinally using (1) psychophysical testing of olfactory detection, discrimination and identification performance and (2) the recording of olfactory event-related brain potentials. Time-frequency analysis was used to enhance the signal-to-noise ratio of the electrophysiological responses. Psychophysical and electrophysiological assessment of auditory and trigeminal chemosensory function served as controls. Results: As compared to AC and OD, MCI patients exhibited a significant asymmetry of olfactory performance. This asymmetry efficiently discriminated between MCI and AC (sensitivity: 85% , specificity: 77% ), as well as MCI and OD (sensitivity: 85% , specificity: 70% ). There was also an asymmetry of the electrophysiological responses, but not specific for MCI. In both MCI and OD, olfactory stimulation of the best nostril elicited significantly more activity than stimulation of the worse nostril, between 3–7.5 Hz and 1.2–2.0 s after stimulus onset. Trigeminal and auditory psychophysical testing did not show any difference between groups. Conclusion: MCI patients exhibit a marked asymmetry of behavioral olfactory function, which could be useful for the diagnostic workup of MCI.

Keywords: Alzheimer’s disease, EEG, evoked potentials, mild cognitive impairment, olfaction, smell

DOI: 10.3233/JAD-141494

Journal: Journal of Alzheimer's Disease, vol. 47, no. 1, pp. 253-270, 2015